1. Field of the Invention
This invention relates to a capacity control valve device for variable capacity swash plate compressors, and more particularly to a capacity control valve device of this kind, which changes the stroke of pistons of a variable capacity swash plate compressor to thereby control delivery quantity of the variable capacity swash plate compressor.
2. Description of the Prior Art
FIGS. 1 and 2 are conceptual views showing a conventional capacity control valve device of a variable capacity swash plate compressor. FIG. 1 shows the capacity control valve device in a state in which the valve opening of a main valve thereof is small, and FIG. 2 shows the capacity control valve device in a state in which the valve opening of the main valve is large.
The capacity control valve device is arranged within a rear head 103 of the variable capacity swash compressor. As shown in FIG. 1, the capacity control valve device is comprised of a main valve 130 having a valve element 131 and a spring 132 for urging the valve element 131 in a valve-opening direction (downward as viewed in FIG. 1), an accumulator 133 for accumulating high-pressure refrigerating gas therein to build up pressure for urging the valve element 131 in a valve-closing direction, a high-pressure passage 134 for introducing the high-pressure refrigerant gas from a discharge chamber 112 into the accumulator 133, a pilot valve 140 arranged at an intermediate portion of the high-pressure passage 134 for controlling a flow rate of the high-pressure refrigerant gas flowing into the accumulator 133 in dependence on pressure in a suction port 103a, the pilot valve having a valve element 135 and a spring 125 for urging the valve element 135 in a valve-closing direction (i.e. upward as viewed in FIG. 1), and a pressure control passage 131a formed through the valve element 131 for permitting the high-pressure refrigerant gas within the accumulator 133 to escape to a suction chamber 113.
The suction port 103a is constantly communicated with a crank case (not shown), and the pressure in the suction port 103a and pressure within the crank case are maintained equal to each other.
When thermal load on the compressor decreases to decrease the pressure Pe in the suction port 103a, the pilot valve 140 is opened, as shown in FIG. 1, to permit the high-pressure refrigerant gas to flow from the discharge chamber 112 into the accumulator 133 through the high-pressure passage 134. Part of the high-pressure refrigerant gas which has flowed into the accumulator 133 escapes to the suction chamber 113 via the pressure control passage 131a formed through the valve element 132. However, the flow rate of high-pressure refrigerant gas which escapes from the accumulator 133 is smaller than that of high-pressure refrigerant gas flowing therein, so that the pressure within the accumulator 133 builds up. Further, when the pressure Pe in the suction port 103a decreases, force urging the valve element 131 downward, i.e. in the valve-opening direction decreases, whereby the valve element 131 is moved upward i.e. in the valve-closing direction to reduce the valve opening of the main valve 130. The valve element 131 of the main valve 130 is thus moved in the valve-closing direction up to a position in which the pressure within the accumulator 133 and the sum of the pressure Pe in the suction port 103a and urging force Fp of the spring 125 become equal to each other.
The condition in which the pressure Pe in the suction port 103a is low (see FIG. 1) can be expressed as follows: EQU Pd.times.Sd&gt;Pe.times.Se+Fp
where Pd: pressure within the discharge chamber, Sd: a pressure-receiving area of the valve element of the pilot valve on the Pd side, Pe: pressure in the suction port, Se: a pressure-receiving area of the valve element of the pilot valve on the Pe side, and Fp: urging force of the spring.
On the other hand, when the thermal load on the compressor increases to increase the pressure in the suction port 103a, the pilot valve 140 is closed, as shown in FIG. 2, to cut off the flow of the high-pressure refrigerant gas from the discharge chamber 112 to the accumulator 133, so that the pressure within the accumulator 133 is progressively reduced as the high-pressure refrigerant gas within the accumulator escapes to the suction chamber 113 through the pressure control passage 131a of the valve element 131. As a result, the valve element 131 of the main valve 130 is moved in the valve-opening direction (downward as viewed in FIG. 2) to increase the valve opening of the main valve 130, whereby the flow rate of refrigerant gas from the suction port 103a to the suction chamber 113 is increased.
The condition in which the pressure Pe in the suction port 103a is high (see FIG. 2) can be expressed as follows: EQU Pd.times.Sd&lt;Pe.times.Se+Fp
As described above, according to the conventional capacity control valve device, when the pilot valve 140 opens, the high-pressure refrigerant gas flows from the discharge chamber 133 into the accumulator 112 through the high-pressure passage 134. However, since part of the high-pressure refrigerant gas flowing into the accumulator 133 escapes to the suction chamber 113 through the pressure control passage 131a, the pressure within the accumulator 133 rises slowly. Therefore, it takes a considerable time period before the valve element 131 of the main valve 130 is moved in the valve-closing direction to decrease the valve opening the main valve 130, which results in degraded response of the device.
Further, according to the above capacity control valve device, when the pilot valve 140 closes, the flow of high-pressure refrigerant gas from the discharge chamber 112 to the accumulator 133 is cut off, and the high-pressure refrigerant gas within the accumulator 133 escapes to the suction chamber 113 through the pressure control passage 131a, whereby the pressure within the accumulator 133 is reduced. However, the pressure within the accumulator 133 decreases slowly, and hence it takes a considerable time period before the valve element 131 is moved in the valve-opening direction to increase the valve opening of the main valve 130, which also results in degraded response of the device.